The present invention relates to a semiconductor photodetector including a semiconductor light receiving element having spectral sensitivity to light in wavelengths from the visible light region to the infrared region and an optical transmitting resin where micro particles which block light in wavelengths in the infrared region are dispersed in a transparent resin, and having spectral sensitivity to light in wavelengths in the visible light region.
As an illumination sensor which is a type of a photodetector in the visible light region, a CdS cell having spectral sensitivity characteristics as shown in FIG. 11 has been widely used. However, since cadmium is high in environmental burdens and falls under a controlled substance by RohS command of EU, cadmium will be prohibited to use within EU from July 2006. As a replacement of cadmium, photodetectors formed from silicon have attempted to be used. In order to compose an illumination sensor with silicon, spectral sensitivity of silicon needs to be coordinated with relative luminous characteristics which are sensitivity of human eyes. FIG. 12 shows spectral sensitivity characteristics of a silicon phototransistor. From FIG. 12, it is grasped that the silicon phototransistor has sensitivity to light in wavelengths of at least 800 nm (infrared region). On the other hand, human eyes do not have sensitivity to the light in the infrared region as shown in standard relative luminous characteristics in FIG. 13.
From the above-mentioned reason, a conventional photodetector of such type is provided with a filter composed of multilayer film in which an oxide silicon (SiO2) film and a titanium oxide (TiO2) film are alternatively laminated at a light receiving surface side to lower spectral sensitivity of the infrared region within the spectral sensitivity of silicon, to thereby approximate to relative luminous characteristics (FIG. 13) (see, for example Japanese Unexamined Patent Publication No. 15044/1997).
However, formation of the multilayer film in which an oxide silicon film and a titanium oxide film are alternatively laminated is a troublesome task in terms of time and processes, and results in high cost. Therefore, the applicant of the present invention has been proposed a semiconductor photodetector having spectral sensitivity characteristics close to relative luminous characteristics at low cost (Japanese Unexamined Patent Publication No. 12885/2005).
The semiconductor having been previously proposed by the applicant of the present invention is shown in FIG. 14. In FIG. 14, numeral 1 is a substrate, 2 is a semiconductor light receiving element having high spectral sensitivity in wavelengths from at least the visible light region to infrared region, 3 is a metal wire, and 4 is an optical transmitting resin in which the optical transmitting resin is boride of one or more elements selected from La, Pr, Nd, Ce, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo or W and is formed by dispersing micro particles whose particle diameter is not more than approximately 100 nm in a transparent resin. By sealing at least the light receiving surface of the semiconductor light receiving element 2 with the optical transmitting resin 4 in which micro particles are dispersed, the micro particles attenuate the light in wavelengths of the infrared region of the incident light to achieve spectral sensitivity characteristics which close to relative luminous characteristics.
However, in the case of dispersing micro particles with the quantity for blocking light in the infrared region in a transparent resin, the semiconductor photodetector previously proposed by the applicant of the present invention also blocks light in the visible light region when the quantity of micro particle is too much. Therefore, output of a semiconductor light receiving element (photocurrent) becomes small.
In specific, FIG. 15 shows changes of transmissivity when the quantity of micro particles (lanthanum boride) to be dispersed in a transparent resin (epoxy resin) is changed. The optical transmitting resin is prepared by mixing a suspension in which micro particles are suspended in an organic solvent such as toluene with the transparent resin (epoxy resin). Therefore, the quantity of micro particles to be dispersed is increased with the increased quantity of suspension. From the figure, it is grasped that light in the visible light region is correspondingly blocked when the transmissivity of light in the infrared region decreased. It has been also confirmed that light in the visible light region is blocked together with the decrease in transmissivity of light in the infrared region in the case the thickness of the resin is increased.
FIG. 16 shows the relative transmissivity when the peak value of transmissivity of an optical transmitting resin with a thickness of 1 mm which includes 2.0 wt. % of suspension of lanthanum boride is 100%. Compared with the relative luminous sensitivity, the optical transmitting resin transmits light in the infrared region.
When a semiconductor photodetector is formed by using such optical transmitting resin, no problem occurs by fluorescent light which does not include light in wavelengths of the infrared region in which light receiving sensitivity of the semiconductor light receiving element is high. However, photocurrent may be generated by incidence of light in the infrared region by sunlight which includes light in wavelengths in the infrared region.
Accordingly, when the quantity of micro particles is increased enough to substantially block light in the infrared region, light in wavelengths of the visible light region is blocked and photocurrent of a semiconductor light receiving element (output signal) becomes significantly small. In such a case, there is a need for additionally providing an amplifying means for an output signal.
There has been a problem that cost is increased in the case of additionally providing such amplifying means for an output signal. On the other hand, there has been also a problem that relative luminous characteristics cannot be obtained when a semiconductor photodetector is formed to transmit light in the infrared region to some extent. An object of the present invention is to resolve the above-mentioned problems and to provide a semiconductor photodetector which can achieve spectral sensitivity characteristics close to relative luminous characteristics compared to a conventional semiconductor photodetector at low cost.